Puzzle of collective enhancement in the nuclear level density

Pandit, Deepak; Dey, Balaram; Bhattacharya, Srijit; Rana, T. K.; Mondal, Debashis; Mukhopadhyay, S.; Pal, Surajit; De, A.; Roy, Pratap; Banerjee, K.; Kundu, S.; Sikdar, A. K.; Bhattacharya, C.; Banerjee, S.

doi:10.1016/j.physletb.2021.136173

Cited by 11 publications

(4 citation statements)

References 40 publications

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“…This leads to an increase in the centroid energy of the GDR and, hence, the symmetry energy of medium and heavy mass nuclei also increases by approximately 8% at T ≈ 1 MeV [55]. In the current work, we notice a slight increase of 3-5% in the centroid energy at T ≈ 0.7 -1 MeV as compared with the ground-state values for nearly-spherical 120 Sn [57], 208 Pb [58] and 201 Tl [50] nuclei as well as for the deformed nuclei in the A = 160 -180 mass region [41,51,52]. Although such an increase is within the experimental errors, it leads to a distinct systematic behaviour, as shown in the right panel of Fig.…”

supporting

confidence: 50%

“…9, the right panel of Fig. 3 shows a sym (A) values for GDRs built on excited states in slightly-deformed nuclei 31 [46], 63 Cu [47], 97 Tc [48], 120 Sn [49] and Tl as well as for well-deformed nuclei in the A ≈ 160 -180 mass region ( 158,160,166 Er, 169 Tm and 185 Re [41,51,52]). With an average temperature between T ≈ 0.7 and 1.0 MeV and below J c , these nuclei were selected to investigate the symmetry energy at temperatures relevant to the r-process nucleosynthesis.…”

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confidence: 99%

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Enhanced symmetry energy bears universality of the r-process

Orce,

Dey,

Ngwetsheni

et al. 2021

Preprint

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The abundance of about half of the stable nuclei heavier than iron via the rapid neutron capture process or r-process is intimately related to the competition between neutron capture and β -decay rates, which ultimately depends on the binding energy of neutron-rich nuclei. The well-known Bethe-Weizsäcker semi-empirical mass formula [1,2] describes the binding energy of ground states -i.e. nuclei with temperatures of T ≈ 0 MeV -with the symmetry energy parameter converging between 23 -27 MeV for heavy nuclei. Here we find an unexpected enhancement of the symmetry energy at higher temperatures, T ≈ 0.7 -1.0 MeV, from the available data of giant dipole resonances built on excited states. Although these are likely the temperatures where seed elements are created -during the cooling down of the ejecta following neutron-star mergers[3] or collapsars[4] -the fact that the symmetry energy remains constant between T ≈ 0.7 -1.0 MeV, suggests a similar trend down to T ≈ 0.5 MeV, where neutron-capture may start occurring. Calculations using this relatively larger symmetry energy yield a reduction of the binding energy per nucleon for heavy neutron-rich nuclei and inhibits radiative neutron-capture rates. This results in a substantial close in of the neutron dripline -where nuclei become unbound -which elucidates the long sought universality of heavyelement abundances through the r-process; as inferred from the similar abundances found in extremely metal-poor stars and the Sun.

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confidence: 50%

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confidence: 99%

Enhanced symmetry energy bears universality of the r-process

Orce,

Dey,

Ngwetsheni

et al. 2021

Preprint

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“…There is bountiful information for T ? 1 MeV from heavy-ion fusion-evaporation reactions [25][26][27][28], some in the range 0.7 T 1 MeV [29][30][31][32][33][34][35], and hardly anything for 0 T < 0.7 MeV. At T ≈ 0 MeV, α E1 has been determined from Coulomb-excitation reactions for only a couple of favorable cases with excited states J = 1/2-7 Li [36][37][38] and 17 O [39]-where the spectroscopic or static quadrupole moment is zero, Q S (J = 1/2) = 0 3 .…”

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confidence: 99%

Electric dipole polarizability of low-lying excited states in atomic nuclei

Orce,

Ngwetsheni

2024

J. Phys. G: Nucl. Part. Phys.

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New equations for the electric dipole polarizability αE1 of low-lying excited states in atomic nuclei — and the related (–2) moment of the total photo-absorption cross section, σ–2 — are inferred in terms of electric dipole and quadrupole matrix elements. These equations are valid for arbitrary angular momenta of the initial/ground and final/excited states and have been exploited in fully converged 1h̄ω shell-model calculations of selected p- and sd-shellnuclei that consider configuration mixing; advancing previous knowledge from 17O to 36Ar, where thousands of electric dipole matrix elements are computed from isovector excitations which include the giant dipole resonance region. Our results are in reasonable agreement with previous shell-model calculations and follow — except for 6,7 Li and 17,18 O — Migdal’s global trend provided by the combination of the hydrodynamic model and second-order non-degenerate perturbation theory. Discrepancies in 6,7Li and 17O arise as a result of the presence of α-cluster configurations in odd-mass nuclei, whereas the disagreement in 18O comes from the mixing of intruder states, which is lacking in the shell-model interactions. More advanced ab initio calculations of the dipole polarizability for low-lying excited states covering all the isovector states within the giant dipole resonance region are missing and could be very valuable to benchmark the results presented here and shed further light on how atomic nuclei polarize away from the ground state

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“…Reliable nuclear level densities are therefore very crucial in the determination of nuclear reaction rates in the field of nuclear astrophysics [4,5]. In addition, the enhancement in the NLD due to collective degrees of freedom (such as rotation and vibration) i.e collective enhancement [6][7][8][9] is another puzzling topic [8]. The collective enhancement present in the NLD, especially around the particle separation energy, could have a significant role in the particle capture cross-sections.…”

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confidence: 99%

Collective enhancement in nuclear level density of $^{72}$Ga and its effect on $^{71}$Ga(n, $γ$)$^{72}$Ga capture cross-section

Santra¹,

Dey²,

Roy³

et al. 2022

Preprint

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The γ-gated proton spectra measured in the reactions 64 Ni( 9 Be, p2n) 70 Ga and 64 Ni( 9 Be, pn) 71 Ga, have been utilized to obtain the nuclear level density (NLD) of 71 Ga and 72 Ga nuclei by using the statistical model (SM) calculations. It is seen that the γ-gated proton spectrum are reasonably explained by using the large value of the inverse level density parameter (k = 11.2 MeV) in the NLD prescription of the Fermi gas (FG) model. The large value of k is indicative of the rotational enhancement, which is consistent with the earlier results in other mass regions. Furthermore, a rotational enhancement factor has been included in the NLD and used in the SM calculation keeping the systematic value of k=8.6 MeV and it explains the γ-gated proton spectrum nicely. The result clearly indicates the presence of collective enhancement in NLD. Subsequently, the NLD with collective enhancement has been utilized in the TALYS calculation, for the first time, to calculate the 71 Ga(n, γ) 72 Ga capture cross-section. It is observed that, while the FG model without the collective enhancement in the NLD for 72 Ga under predicts the capture data, with the rotational enhancement correction the FG model over predicts the data by similar amount at higher energies. However, in the energy range of 0.01 MeV to 0.1 MeV, the FG model corrected for rotational enhancement describes the data quite well. Thus, the present work indicates that collective enhancement, whenever required, should be taken into account fro proper description of low energy capture cross section data.

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Puzzle of collective enhancement in the nuclear level density

Cited by 11 publications

References 40 publications

Enhanced symmetry energy bears universality of the r-process

Enhanced symmetry energy bears universality of the r-process

Electric dipole polarizability of low-lying excited states in atomic nuclei

Collective enhancement in nuclear level density of $^{72}$Ga and its effect on $^{71}$Ga(n, $γ$)$^{72}$Ga capture cross-section

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